[X86] Emulate AVX 256bit MIN/MAX support by splitting the vector.

In AVX 256bit vectors are valid vectors and therefore the Type Legalizer doesn't
split the VSELECT and SETCC nodes. AVX only supports MIN/MAX on 128bit vectors
and this fix enables vector splitting for this special case in the X86 DAG
Combiner.

This fix is related to PR16695, PR17002, and <rdar://problem/14594431>.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191131 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/X86/X86ISelLowering.cpp

@@ -16371,24 +16371,28 @@ static SDValue PerformEXTRACT_VECTOR_ELTCombine(SDNode *N, SelectionDAG &DAG,
 }
 
 /// \brief Matches a VSELECT onto min/max or return 0 if the node doesn't match.
-static unsigned matchIntegerMINMAX(SDValue Cond, EVT VT, SDValue LHS,
+static std::pair<unsigned, bool>
-                                   SDValue RHS, SelectionDAG &DAG,
+matchIntegerMINMAX(SDValue Cond, EVT VT, SDValue LHS, SDValue RHS,
-                                   const X86Subtarget *Subtarget) {
+                   SelectionDAG &DAG, const X86Subtarget *Subtarget) {
   if (!VT.isVector())
-    return 0;
+    return std::make_pair(0, false);
 
+  bool NeedSplit = false;
   switch (VT.getSimpleVT().SimpleTy) {
-  default: return 0;
+  default: return std::make_pair(0, false);
   case MVT::v32i8:
   case MVT::v16i16:
   case MVT::v8i32:
     if (!Subtarget->hasAVX2())
-      return 0;
+      NeedSplit = true;
+    if (!Subtarget->hasAVX())
+      return std::make_pair(0, false);
+    break;
   case MVT::v16i8:
   case MVT::v8i16:
   case MVT::v4i32:
     if (!Subtarget->hasSSE2())
-      return 0;
+      return std::make_pair(0, false);
   }
 
   // SSE2 has only a small subset of the operations.
@@ -16399,6 +16403,7 @@ static unsigned matchIntegerMINMAX(SDValue Cond, EVT VT, SDValue LHS,
 
   ISD::CondCode CC = cast<CondCodeSDNode>(Cond.getOperand(2))->get();
 
+  unsigned Opc = 0;
   // Check for x CC y ? x : y.
   if (DAG.isEqualTo(LHS, Cond.getOperand(0)) &&
       DAG.isEqualTo(RHS, Cond.getOperand(1))) {
@@ -16406,16 +16411,16 @@ static unsigned matchIntegerMINMAX(SDValue Cond, EVT VT, SDValue LHS,
     default: break;
     case ISD::SETULT:
     case ISD::SETULE:
-      return hasUnsigned ? X86ISD::UMIN : 0;
+      Opc = hasUnsigned ? X86ISD::UMIN : 0; break;
     case ISD::SETUGT:
     case ISD::SETUGE:
-      return hasUnsigned ? X86ISD::UMAX : 0;
+      Opc = hasUnsigned ? X86ISD::UMAX : 0; break;
     case ISD::SETLT:
     case ISD::SETLE:
-      return hasSigned ? X86ISD::SMIN : 0;
+      Opc = hasSigned ? X86ISD::SMIN : 0; break;
     case ISD::SETGT:
     case ISD::SETGE:
-      return hasSigned ? X86ISD::SMAX : 0;
+      Opc = hasSigned ? X86ISD::SMAX : 0; break;
     }
   // Check for x CC y ? y : x -- a min/max with reversed arms.
   } else if (DAG.isEqualTo(LHS, Cond.getOperand(1)) &&
@@ -16424,20 +16429,20 @@ static unsigned matchIntegerMINMAX(SDValue Cond, EVT VT, SDValue LHS,
     default: break;
     case ISD::SETULT:
     case ISD::SETULE:
-      return hasUnsigned ? X86ISD::UMAX : 0;
+      Opc = hasUnsigned ? X86ISD::UMAX : 0; break;
     case ISD::SETUGT:
     case ISD::SETUGE:
-      return hasUnsigned ? X86ISD::UMIN : 0;
+      Opc = hasUnsigned ? X86ISD::UMIN : 0; break;
     case ISD::SETLT:
     case ISD::SETLE:
-      return hasSigned ? X86ISD::SMAX : 0;
+      Opc = hasSigned ? X86ISD::SMAX : 0; break;
     case ISD::SETGT:
     case ISD::SETGE:
-      return hasSigned ? X86ISD::SMIN : 0;
+      Opc = hasSigned ? X86ISD::SMIN : 0; break;
     }
   }
 
-  return 0;
+  return std::make_pair(Opc, NeedSplit);
 }
 
 /// PerformSELECTCombine - Do target-specific dag combines on SELECT and VSELECT
@@ -16795,9 +16800,30 @@ static SDValue PerformSELECTCombine(SDNode *N, SelectionDAG &DAG,
   }
 
   // Try to match a min/max vector operation.
-  if (N->getOpcode() == ISD::VSELECT && Cond.getOpcode() == ISD::SETCC)
+  if (N->getOpcode() == ISD::VSELECT && Cond.getOpcode() == ISD::SETCC) {
-    if (unsigned Op = matchIntegerMINMAX(Cond, VT, LHS, RHS, DAG, Subtarget))
+    unsigned Opc;
-      return DAG.getNode(Op, DL, N->getValueType(0), LHS, RHS);
+    bool NeedSplit;
+    std::tie(Opc, NeedSplit) = matchIntegerMINMAX(Cond, VT, LHS, RHS, DAG, Subtarget);
+
+    if (Opc && NeedSplit) {
+      unsigned NumElems = VT.getVectorNumElements();
+      // Extract the LHS vectors
+      SDValue LHS1 = Extract128BitVector(LHS, 0, DAG, DL);
+      SDValue LHS2 = Extract128BitVector(LHS, NumElems/2, DAG, DL);
+
+      // Extract the RHS vectors
+      SDValue RHS1 = Extract128BitVector(RHS, 0, DAG, DL);
+      SDValue RHS2 = Extract128BitVector(RHS, NumElems/2, DAG, DL);
+
+      // Create min/max for each subvector
+      LHS = DAG.getNode(Opc, DL, LHS1.getValueType(), LHS1, RHS1);
+      RHS = DAG.getNode(Opc, DL, LHS2.getValueType(), LHS2, RHS2);
+
+      // Merge the result
+      return DAG.getNode(ISD::CONCAT_VECTORS, DL, VT, LHS, RHS);
+    } else if (Opc)
+      return DAG.getNode(Opc, DL, VT, LHS, RHS);
+  }
 
   // Simplify vector selection if the selector will be produced by CMPP*/PCMP*.
   if (N->getOpcode() == ISD::VSELECT && Cond.getOpcode() == ISD::SETCC &&

test/CodeGen/X86/vec_split.ll

@@ -1,10 +1,14 @@
 ; RUN: llc -march=x86-64 -mcpu=corei7 < %s | FileCheck %s -check-prefix=SSE4
+; RUN: llc -march=x86-64 -mcpu=corei7-avx < %s | FileCheck %s -check-prefix=AVX1
 ; RUN: llc -march=x86-64 -mcpu=core-avx2 < %s | FileCheck %s -check-prefix=AVX2
 
 define <16 x i16> @split16(<16 x i16> %a, <16 x i16> %b, <16 x i8> %__mask) {
 ; SSE4-LABEL: split16:
 ; SSE4: pminuw
 ; SSE4: pminuw
+; AVX1-LABEL: split16:
+; AVX1: vpminuw
+; AVX1: vpminuw
 ; AVX2-LABEL: split16:
 ; AVX2: vpminuw
 ; AVX2: ret
@@ -19,6 +23,11 @@ define <32 x i16> @split32(<32 x i16> %a, <32 x i16> %b, <32 x i8> %__mask) {
 ; SSE4: pminuw
 ; SSE4: pminuw
 ; SSE4: pminuw
+; AVX1-LABEL: split32:
+; AVX1: vpminuw
+; AVX1: vpminuw
+; AVX1: vpminuw
+; AVX1: vpminuw
 ; AVX2-LABEL: split32:
 ; AVX2: vpminuw
 ; AVX2: vpminuw